Machines to crush solid material such as coal, rock and the like are very well known. These machines typically comprise a pair of crushing rolls. These rolls are formed with peripheral crushing teeth. The rolls are spaced apart and rotate towards each other. The solid material passes between the rolls and is crushed to a desired particle size depending, inter alia, on the spacing between the rolls, the size of the teeth and the like.
In these known crushing arrangements, the teeth on one roll are offset with respect to the teeth on the other roll such that the tooth on one of the rolls passes between adjacent teeth on the other roll. This allows a good crushing action to be obtained.
A disadvantage with this type of machine is that product can only be crushed to one size or one size range. Should it be necessary to have product of a different size or size range, it is necessary to provide a separate machine. Alternatively, the rolls need to be adjusted to change the spacing between the rolls. It should be appreciated that adjustment of large and heavy rolls is not an easy task, and it is generally uneconomical to have a number of different machines to provide product of different sizes.
It is known to crush product by a “side sizing” method. These side sizing machines are fairly specialised in design and also crush to a single size. Side sizing requires a single roll and some sort of side plate with the material passing between the single roll and the side plate. The teeth on the roll need to be relatively short and “stubby” in order to provide a good crushing action. This requires a special roll as normal crushing rolls usually have teeth that are much larger.